The present invention is related to a method and apparatus for removing excess plating metal from the edges of electroplated metal strip, and particularly to a method and apparatus for removing excess plated zinc, zinc oxide or zinc alloy from top and bottom surfaces of electrogalvanized steel strip adjacent to the edges thereof and from the narrow face of the strip edges by brushing both the top and bottom surfaces near the edges and the narrow face edge portions of said strip.
In the various processes for the electrodeposition of zinc, zinc oxide or zinc alloys onto steel strip, there is an inherent tendency regardless of the process used to form an excess thickness of plated zinc on the narrow face of the strip edges. The excess thickness of plated zinc results from higher current densities at the narrow face edge of the strip than on the broad strip surface. The higher current density also causes the excess plated zinc to be porous and less adherent to the strip than the more dense uniform plated coating on the broad strip surfaces. If not previously removed, the excess zinc tends to flake and fall off in stamping dies used to form automotive body parts and cause dimples making the stamped parts unusable. In addition, in some electrodeposition processes, zinc is plated onto the top and bottom broad surfaces of the strip near the strip edges particularly on heavier gauge steel strip or that which is side trimmed and does not have a tapered decreasing thickness profile near the strip edges prior to plating. The excess plated zinc on the top and bottom broad surfaces near the edges tends to cause flaring or buildup on the edges of coils wound from the plated strip. This again is a condition that is not acceptable to the customer. For the most critical applications, the customer may request that the plated strip be side trimmed to remove the edges having excess plated metal thereon in order to eliminate the problems it causes them in subsequent operations. This can result in a yield loss of up to 5% significantly increasing cost and causing loss of profit for the steel manufacturer.
U.S. Pat. No. 2,386,663, Deans, discloses an improvement in an edge scraper for removing excess plating metal from the edges of electrolytic tin plated steel strip. This is accomplished by the application of a self-adjusting cutter to the plated strip edges. The cutter includes a freely rotatable hardened steel wheel mounted transversely of the strip on a carriage having wheels riding on longitudinal rails also extending in a transverse direction with respect to the strip. The wheel is urged with equal cutting pressure at all times against the strip by a cable weight and pulley arrangement mounted on the carriage. Air nozzles directed toward the strip edges remove particles of plating metal scraped from the strip and direct them to box-like collectors substantially enclosing the wheels. The collectors are connected to discharge chutes leading to a hopper beneath the carriage base. The problem with this roll-type cutter and other types of cutters such as blade cutters is that plating metal tends to buildup on the cutting face very quickly dulling the cutting tool. Once dull, the tool tends to smear the plated metal producing a rough edge which can lead to customer rejections.
It is also known to use a drag bar or a rotating roll for the purpose of removing excess zinc from the edge of electrogalvanized steel strip. The drag bar smears the zinc particles across the strip edge and extrudes the zinc above and below the strip thickness resulting in flared edges on coils wound from the strip and customer rejection. Drag bars also distort and produce a rough edge. Similarly, the rotating roll compresses loose zinc particles on the edge and distorts and smears the zinc also. The compressed zinc particles tend to fall off as dust and get into stamping dies and onto the strip surface as mentioned above. Also, the smeared zinc provides a rough and flared edge on the coils.
In the manufacture of a metal foil, the burnishing or buffing of the foil after it is electrodeposited onto a mandrel is disclosed in U.S. Pat. No. 2,203,253. This reference discloses a steel roll which contacts the foil and is rotatably driven at a speed about 15% higher than the surface speed of the mandrel so as to smooth the spongy outer surface of the metal foil electrodeposited thereon. U.S. Pat. No. 3,416,207 discloses in the making of electrical capacitors complete removal of a portion of a plated metal surface by grinding.
U.S. Pat. No. 1,473,060, Taylor, discloses a brush which is mounted in a plating tank so as to revolve around a cylindrical cathode immersed in the bath and remove bubbles and solid impurities from the plated deposit on the cathode. The purpose is to prevent the formation of pits in the plated surface. The brushing is done only intermittently for short periods between rather longer periods in which the bath and article to be plated are permitted to remain quiescent. Also, a brush is disclosed in U.S. Pat. No. 1,494,152, Cowper-Coles, in a method of making wire by electrodeposition of metal onto a rotating cylinder. On an upper surface of the horizontal cylinder which is above the level of the bath, a brush is located to brush the deposit as it emerges from the electrolyte. The purpose of the brush is not specifically disclosed. It appears to be a stationary, non-rotatable type for sweeping foreign particles from the plated deposit.